1. Field of the Invention
The present invention relates to an ignition device for a vaporizing type liquid fuel combustion apparatus.
2. Description of Prior Art
There have been proposed igniting devices utilizing spark discharge mechanisms as shown in FIG. 1 and FIG. 2 or an ignition heater as shown in FIG. 3.
In FIG. 1, reference numeral 3 designates the wall of a carburetor. A nozzle 1 is attached to a side surface of the carburetor wall 3. A needle 2 is inserted in the central part of the nozzle 1. The carburetor wall 3 is surrounded by a cover 4. A preheater 5 is embeded in the carburetor wall 3 when the carburetor body is formed by casting. A partition plate 6 is fitted at the upper part of the carburetor wall 3; a rectifying plate 7 is placed above the partition plate 6 and a flame plate 8 provided with flame outlets is placed above the rectifying plate 7. An ignition plug 9 is attached to the cover 4 with the discharging part directed to a flame outlet of the flame plate 8. A flame rod 10 is attached to the cover 4 so as to oppose the ignition plug 9 and is placed in such a manner that the free end of the flame rod is strucked with flame coming from the flame outlet.
In FIG. 2, reference numeral 30 designates a commercial power source for domestical use of 100 V, 50 Hz or 60 Hz. A controller 12 is connected to the power source 30 and a power source switch 11 in series. The controller 12 is connected to the coil side of relays 13, 14, 15 and 16 respectively. The connection is shown in FIG. 2 and deleted in further figures for clarity. A blower motor 17 for feeding air for combustion is connected in series to the contact side of the relay 13. A preheater 5 is connected in series to the contact side of the relay 14. An electromagnetic pump 18 is connected in series to the contact side of the relay 15. There is provided an ignition transformer 19 whose terminal is connected to the relay 16 on the primary side thereof and whose terminal at the secondary side is connected to the ignition plug 9 to produce a voltage of about 1500 V.
The operation of the ignition device having the construction as above-mentioned will be described.
When the power source switch 11 is operated, the relay 14 is turned on through the controller 12 to initiate current conduction of the preheater 5. When temperature of the carburetor wall 3 reaches approximately 200.degree. C., the relay 13 and the relay 15 are turned on through the controller 12 to initiate supply of oil through the electromagnetic pump 18 and whereby air for combustion is supplied by the blower. Oil and air thus supplied are ejected to the inside of the carburetor wall 3 through the needle 2 and the nozzle 1. During the ejection, kerosene is atomized by the shearing force imparted by air and is vapourized due to the carburetor wall 3 which has been preheated to about 200.degree. C., whereby an air-fuel mixture is produced. The mixture is ejected from the flame plate 8 through the partition plate 6 and the rectifying plate 7. At the same time as the ejection of the mixture, the relay 16 is turned on by the controller 12. A high voltage is then applied to the ignition plug 9 from the ignition transformer 19 causing an electric discharge whereby the air-fuel mixture ejected from the flame plate 8 is ignited. When combustion is started, a reduction in the electric impedance exists between the flame rod which is positively charged by the controller 12 and the flame plate 8 which is negatively charged. Accordingly, the controller 12 causes the relay 16 to turn off thereby stopping the electric discharge. Thus, operations are carried out in the sequential order as above-mentioned.
In the conventional ignition device utilizing spark discharge, there are problems of the generation of noise due to the electrical discharge and of difficulty in firing in the case of the mixture having a low concentration or a low temperature region.
FIG. 3 shows a conventional ignition device utilizing an ignition heater. In FIG. 3, reference numeral 30 designates a power source similar to that in FIG. 2; numeral 31 designates a voltage drop transformer connected to the power source 30, numeral 32 designates an ignition heater and numeral 33 designates a switch.
For the ignition heater 32, a nichrome wire or an iron-chromium wire having a diameter as thick as possible is required so that a large current can be passed, surface temperature of about 1000.degree. C. can be obtained and anti-oxidation or corrosion and ignition characteristics can be assured. Further, it is necessary to use the voltage-dropping transformer 31 which reduces voltage to about 20 V. Further, when the ignition heater 33 is directly connected to the 100 V power source 30, a large current flows because of a high voltage thereby causing burning of the heater. Although the problem of burning of the heater can be overcome by using a nichrome wire having a small diameter with an attendant reduction in voltage, the above-mentioned purpose is not satisfied by the use of a thin wire. Accordingly, the voltage-dropping transformer 31 is needed. Thus, in the conventional spark discharge type ignition device, a booster transformer is required to obtain a high voltage and in the conventional ignition heater type firing device, a voltage-dropping transformer is required to obtain a low voltage. Provision of the transformers in the firing devices increase the manufacturing cost of the devices.